Portable telephone

ABSTRACT

A portable phone comprises an upper casing  11  provided with a speaker  14  and a display screen  15 , a lower casing  12  on which a keyboard is disposed  18 , and an antenna  16  mounted on an upper end of the upper casing  11  or a lower end of the lower casing  12 . A dielectric member  17  with a predetermined dielectric constant and little loss is mounted on a back side or a front side of the antenna  16 . The dielectric member  17  may have a curved surface on a side opposite to the antenna  16.

TECHNICAL FIELD

The present invention relates to a portable telephone, and inparticular, it relates to a portable telephone having improvedantenna-based communication performance.

BACKGROUND ART

Compact and built-in antennas are now in increasing demand as recentportable telephones are decreased in size. Known portable telephoneantennas include linear antennas such as a monopole antenna, a helicalantenna, and an inverted-L-shape antenna.

FIGS. 14A and 14B are a front view and a side view of a related-artfolding portable telephone, respectively, as an example. As shown inFIGS. 14A and 14B, the related-art portable telephone 60 includes anupper casing 11 and a lower casing 12 that construct the body of theportable telephone 60, a hinge 13 that joins the upper casing 11 and thelower casing 12 so as to fold or open the portable telephone body, andan antenna 16 for transmission and reception provided to the uppercasing 11. The upper casing 11 includes a speaker 14 and a displayscreen 15 in addition to an internal circuit. The lower casing 12includes a keyboard 18 and a microphone 19 in addition to an internalcircuit. Although the antenna 16 is generally disposed at the upper endof the upper casing 11, it may be disposed at the lower end. The antenna16 is fixed in length but may be varied in length.

The casing accommodates a printed circuit board (not shown), and has atransmission section for supplying transmission power, a powertransmission section that transmits the power to the antenna, and apower amplifier that amplifies the power on the circuit board. Thetransmission power is generally sent from the output terminal of thepower amplifier to the antenna 16 via a feeding section.

FIGS. 15A to 15C are diagrams of concrete examples of the linearantenna. As shown in FIGS. 15A to 15C, linear antennas 16 a to 16 c area monopole antenna, a helical antenna, and an inverted-L-shape antennafrom the top. The monopole antenna 16 a and the helical antenna 16 b,shown in FIGS. 15A and 15B, respectively, are mounted on the top of theportable telephone casing in such a manner that they project therefrom;the inverted-L-shape antenna 16 c shown in FIG. 15C is mounted along thetop or bottom of the casing, having a structure suitable for a built-inantenna.

FIGS. 16A and 16B are front view and side view of another related-artfolding portable telephone, respectively. As shown in FIGS. 16A and 16B,the portable telephone 70 has an antenna built-in structure, in which anupper casing 21 including a printed circuit board 24 and a lower casing22 including a printed circuit board 24 are joined together with a hinge23. The portable telephone 70 has an inverted-L-shaped antenna 26 builtin the lower casing 22.

Since portable telephones are decreasing in size as compact and built-inantennas are increasingly provided, the relative distance between thehead or hand of a talker and the antenna is decreased, so that part ofelectricity radiated from the antenna during talking is absorbed by thehead or hand of the talker, so that the communication performance oftelephones tends to decrease.

In order to overcome the problem, conventional portable telephonetechnology has proposed a method for preventing the decrease incommunication performance by a structure in which an antenna which isreduced in size by decreasing the wavelength owing to the use of adielectric member is disposed at a position higher than a portabletelephone casing via a rod so that the distance between a human body andthe antenna is increased. Such a method is disclosed, for example, inJapanese Unexamined Patent Application Publication No. 2001-94323 (P. 3,FIG. 1).

However, such a structure and a method are not suitable for decreasingthe size of portable telephones including an antenna and having anantenna built-in, because the shape is the same as that of a commondipole antenna having a small antenna thereon.

The above-described related-art portable telephone have the problem ofdifficulty in maintaining communication performance as portabletelephones if the antennas are made more compact or built in.

DISCLOSURE OF INVENTION

The present invention has been made to solve the above problems, and hasas a first object the provision of a portable telephone having astructure suitable for miniaturization and having a built-in antenna,and as a second object the provision of a portable telephone havinghigher communication performance during talking with such a structure.

A portable telephone according to the present invention is characterizedin that a dielectric member with a relatively high dielectric constantand little loss is mounted to the part of an antenna adjacent to thehead of a talker, or at a position opposite to a part covered by thepalm of the hand, wherein electromagnetic fields due to transmitted andreceived electric waves are concentrated on the dielectric member, or insome cases, a curved surface is provided on the dielectric member,thereby allowing electromagnetic waves to pass therethrough to provide adirectivity opposite to the human body.

Other objects, structures, and advantages of the present invention willbe more apparent by referring to the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a front view and a side view of a portable telephoneaccording to a first embodiment of the present invention, respectively;

FIGS. 2A and 2B are a front view and a side view of a portable telephoneaccording to a second embodiment of the present invention, respectively:

FIG. 3 is a side view of a portable telephone according to a thirdembodiment of the present invention;

FIG. 4 is a side view of a portable telephone according to a fourthembodiment of the present invention;

FIGS. 5A to 5C are diagrams showing various shaped dielectric membersused in FIGS. 1 to 4;

FIG. 6 is an explanatory diagram of the three-dimensional orthogonalcoordinates of a linear antenna model for explaining the principle ofthe present invention;

FIG. 7 is a characteristic diagram of the amount of electromagneticenergy plotted against the relative dielectric constant of FIG. 6;

FIG. 8 is an enlarged view of a dielectric member for explaining arefraction phenomenon around the critical angle of electromagnetic wavesradiated from the antenna to a finite-thickness dielectric member inFIG. 6;

FIG. 9 is an enlarged view of a dielectric member for explaining areflection and refraction phenomenon at the end of the dielectric membercaused by a surface wave component traveling in the dielectric member inFIG. 8;

FIG. 10 is an enlarged view of a dielectric member for explaining adirection in which an electromagnetic wave travels when the dielectricmember in FIG. 6 has a curved surface;

FIGS. 11A and 11B are a front view and a side view of a portabletelephone for explaining a simulation model in which aninverted-L-shaped antenna is used in FIGS. 3 and 4;

FIG. 12 is a perspective view of a portable telephone for explaining thesimulation model in which the palm and fingers of the talker areimitated in FIG. 11;

FIG. 13 is a characteristic diagram of the relationship between relativedielectric constants and electromagnetic radiation efficiencies forexplaining the analysis of the simulation model in FIGS. 11 and 12;

FIGS. 14A and 14B are a front view and a side view of a related-artfolding portable telephone, respectively;

FIGS. 15A to 15C are diagrams of concrete examples of common linearantennas; and

FIGS. 16A and 16B are a front view and a side view of anotherrelated-art folding portable telephone, respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described hereinbelow.

A portable telephone according to the present invention includes adielectric member having a relatively high relative dielectric constantand little loss in the vicinity of an antenna and opposite to a partcovered with the head or the flat part of the hand of a talker, theelectromagnetic field of a near-field region is concentrated on thedielectric member section, and in some cases, the dielectric member isgiven a curved surface, allowing electromagnetic waves to pass throughoutward to provide a directivity opposite to the human body, thusachieving an antenna with a small power loss due to a human body. Thisprovides a portable telephone that has an antenna gain higher than thatof conventional ones, improving the talking characteristic as a portabletelephone.

Embodiments of the present invention will be described with reference tothe drawings.

FIRST EMBODIMENT

FIGS. 1A and 1B are a front view and a side view of a portable telephoneaccording to a first embodiment of the present invention. As shown inFIGS. 1A and 1B, a portable telephone 10 according to this embodimentincludes an upper casing 11 and a lower casing 12 that construct thebody of the portable telephone, a hinge 13 that joins the upper casing11 and the lower casing 12 so as to fold or open the portable telephonebody, an antenna 16 for transmission and reception provided to the uppercasing 11, and a dielectric member 17 disposed on the back of theantenna 16. The dielectric member 17 reduces a power loss due to thehead of a talker to improve communication performance.

The upper casing 11 includes a speaker 14 and a display screen 15 inaddition to an internal circuit, and the lower casing 12 includes akeyboard 18 and a microphone 19 in addition to an internal circuit, asin the above-described related art (FIG. 14).

Although the antenna 16 is generally disposed at the upper end of theupper casing 11, it may be disposed at the lower end. The antenna 16 isfixed in length but may be varied in length.

The casing accommodates a printed circuit board (not shown), and has atransmission section for supplying transmission power, a powertransmission section that transmits the power to the antenna, and apower amplifier that amplifies the power on the circuit board. Thetransmission power is generally sent from the output terminal of thepower amplifier to the antenna 16 via a feeding section.

In short, the antenna 16 of the portable telephone according to thisembodiment is characterized by including the dielectric member 17 havinga higher relative dielectric constant and lesser loss than the antennaof the related-art portable telephone (FIG. 14). Although the antenna 16and the dielectric member 17 are disposed at the upper end of the uppercasing 11 in FIGS. 1A and 1B, they may be disposed at the lower end ofthe lower casing 12.

SECOND EMBODIMENT

FIGS. 2A and 2B are a front view and a side view of a portable telephoneaccording to a second embodiment of the present invention. As shown inFIGS. 2A and 2B, in this embodiment, the antenna 16 and the dielectricmember 17 are disposed at the lower end of the lower casing 12 to reducethe influence of the palm of a hand.

In that case, the dielectric member 17 is disposed on the antenna fromthe front of the portable telephone 10, as shown in FIGS. 2A and 2B.

While in the first and second embodiments the antenna 16 projectsoutward from the casings 11 and 12, it may be built in the casing.

Although the antenna 16 has a monopole antenna structure in FIGS. 1A,1B, 2A and 2B, it may have an inverted-L-shaped antenna structure. Also,while the dielectric member 17 is in shape of a hemisphere shape, it maybe a dielectric member in shape of rectangular, a dielectric member inshape of hemicylinder, or other shapes having a curved surface.

THIRD EMBODIMENT

FIG. 3 is a side view of a portable telephone according to a thirdembodiment of the present invention. As shown in FIG. 3, a portabletelephone 10 according to this embodiment has an antenna 16A and adielectric member 17A on the upper casing or an antenna 16B and adielectric member 17B on the lower casing. FIG. 3 shows the positionalrelationship between the head X and the palm Y of a talker. In thiscase, the antenna 16A and the dielectric member 17A can be replaced withthe antenna 16B and the dielectric member 17B, only by the detachmentthereof.

FOURTH EMBODIMENT

FIG. 4 is a side view of a portable telephone according to a fourthembodiment of the present invention. As shown in FIG. 4, a portabletelephone 20 according to this embodiment has a structure in which theupper casing 21 and the lower casing 22 can be folded with the hinge 23and antennas 26A and 26B and dielectric members 27A and 27B are builtin.

In this case, the upper casing 21 includes the printed circuit board 24,at the upper end of which the antenna 26A and the dielectric member 27Aare mounted.

Similarly, the lower casing 22 may include the printed circuit board 24,at the lower end of which the antenna 26B and the dielectric member 27Bmay be mounted.

In order to minimize the thickness of the portable telephone 20 of thisembodiment, for the upper casing 21, the antenna 26A and the dielectricmember 27A have only to be disposed on the front surface of the printedcircuit board 24, or at a position close to the head X of the talkerand, for the lower casing 22, the antenna 26B and the dielectric member27B have only to be disposed on the back of the printed circuit board24, or at a position close to the palm Y of the talker.

FIGS. 5A to 5C are diagrams showing various shaped dielectric membersused in FIGS. 1 to 4. FIG. 5A shows an example in which a dielectricmember in shape of rectangular 28 is used for the antenna 16. Numeral 29denotes a joint with the casing of the portable telephone or a built-inboard, serving as a feeding section for electricity supplied by theportable telephone body to the antenna 16.

Likewise, FIG. 5B shows an example in which a dielectric member in shapeof hemisphere 30 is used for the antenna 16, and FIG. 5C shows anexample in which a dielectric member in shape of hemicylinder 31 isused.

While the antenna 16 is a monopole antenna by way of example, aninverted-L-shaped antenna can also be mounted.

The principle of operation of the antenna having a dielectric memberaccording to this embodiment will be described with reference to FIGS. 6to 13.

FIG. 6 is an explanatory diagram of the three-dimensional orthogonalcoordinates of a linear antenna model for explaining the principle ofthe present invention. As shown in FIG. 6, when the antenna 16 ismounted on a hemi-infinite space, on a dielectric member (dielectricconstant: ε1) 32 in this case, most of the electromagnetic wavesradiated from the antenna 16 having a length L are concentrated on thedielectric member 32, where ε0 is a dielectric constant in a vacuum.

In the three-dimensional orthogonal coordinate system, the lowerhemisphere (z<0) is a hemi-infinite space (dielectric constant: ε1)having a relative dielectric constant εr=(ε1/ε0) [>1], and the upperhemisphere (z>0) is a vacuum hemi-infinite space (dielectric constant:ε0). The magnetic permeability is μ0 in the whole space. The antenna 16is an L-long linear antenna located at the origin and in parallel withthe x-axis. Suppose that a high-frequency current i having an angularfrequency ω flows on the antenna 16.

In such a state, both of a magnetic wave 33 radiated to the upperhemisphere and a magnetic wave 34 radiated to the lower hemisphere willbe discussed. The z-components of the electric field and the magneticfield in the position (x, y, z) of z>0 or z<0, or Ez and Hz, areexpressed as equation (1) by plane-wave decomposition (refer to Chew“Waves and Fields in Inhomogeneous Media,” IEEE, ISBN 0-7803-4749-8):$\begin{matrix}\begin{matrix}\left. \begin{matrix}{E_{Z} = {\left( \frac{l1}{8\quad\pi^{2}\omega\quad ɛ_{0}} \right)\quad\underset{{{- \infty} < k_{x}},{k_{y} < \infty}}{\int\int}k_{x}{\exp\left( {{{\mathbb{i}}\quad k_{x}x} + {{\mathbb{i}}\quad k_{y}y} + {{\mathbb{i}}\quad k_{0z}z}} \right)}\left\{ {1 - R^{TM}} \right\}\quad{\mathbb{d}k_{x}}\quad{\mathbb{d}k_{y}}}} \\{H_{z} = {\left( \frac{l1}{8\quad\pi^{2}} \right)\quad\underset{{{- \infty} < k_{x}},{k_{y} < \infty}}{\int\int}\frac{k_{y}}{k_{0z}}{\exp\left( {{{\mathbb{i}}\quad k_{x}x} + {{\mathbb{i}}\quad k_{y}y} + {{\mathbb{i}}\quad k_{0z}z}} \right)}\left\{ {1 + R^{TM}} \right\}\quad{\mathbb{d}k_{x}}\quad{\mathbb{d}k_{y}}}} \\\left( {z > 0} \right) \\{E_{z} = {\left( \frac{- {l1}}{8\quad\pi^{2}\omega\quad ɛ\quad 1} \right)\quad\underset{{{- \infty} < k_{x}},{k_{y} < \infty}}{\int\int}k_{x}{\exp\left( {{{\mathbb{i}}\quad k_{x}x} + {{\mathbb{i}}\quad k_{y}y} - {{\mathbb{i}}\quad k_{1z}z}} \right)}T^{TM}\quad{\mathbb{d}k_{x}}\quad{\mathbb{d}k_{y}}}} \\{H_{z} = {\left( \frac{l1}{8\quad\pi^{2}} \right)\quad\underset{{{- \infty} < k_{x}},{k_{y} < \infty}}{\int\int}\frac{k_{y}}{k_{1z}}{\exp\left( {{{\mathbb{i}}\quad k_{x}x} + {{\mathbb{i}}\quad k_{y}y} - {{\mathbb{i}}\quad k_{1z}z}} \right)}T^{TM}{\mathbb{d}k_{x}}\quad{\mathbb{d}k_{y}}}} \\\left( {z < 0} \right)\end{matrix}\quad \right\} \\{{where},} \\\begin{matrix}{R^{TM} = \frac{{ɛ_{1}k_{0z}} - {ɛ_{0}k_{1z}}}{{ɛ_{1}k_{0z}} + {ɛ_{0}k_{1z}}}} & \quad & \quad & {R^{TE} = \frac{k_{0z} - k_{1z}}{k_{0z} + k_{1z}}}\end{matrix} \\\begin{matrix}{T^{TM} = \frac{2ɛ_{1}k_{0z}}{{ɛ_{1}k_{0z}} + {ɛ_{0}k_{1z}}}} & \quad & \quad & {T^{TE} = \frac{2k_{0z}}{k_{0z} + k_{1z}}}\end{matrix} \\\begin{matrix}{\quad{k_{0_{z}}^{2} = {k_{0}^{2} - k_{x}^{2} - k_{y}^{2}}}} & \quad & \quad & \quad & {\quad{k_{1_{z}}^{2} = {k_{1}^{2} - k_{x}^{2} - k_{y}^{2}}}}\end{matrix} \\\begin{matrix}{\quad{k_{0} = \sqrt{ɛ_{0}\mu_{0}\omega}}\quad} & \quad & \quad & {{k_{1} = \sqrt{ɛ_{1}\mu_{0}\omega}}\quad}\end{matrix} \\{ɛ_{r} = {\frac{ɛ_{1}}{ɛ_{0}} > 1}}\end{matrix} & (1)\end{matrix}$

If z>0, the component of the integrated term of equation (1) indicates aplane wave that travels in the direction of the wave number vector (kx,ky, k0z), and if z<0, it indicates a plane wave that travels in thedirection of the wave number vector (kx, ky, k1z). R^(TM) and R^(TE)indicate the reflection coefficients of the TM component and the TEcomponent of a plane wave for z=0, respectively, and T^(TM) and T^(TE)indicate the transmission components of the same. The electric fieldsand the magnetic fields Ex, Ey, Hx, and Hy of the x- and y-components ofthe plane-wave components can be obtained by equation (2):$\begin{matrix}\left. \begin{matrix}\begin{matrix}{{{{E_{x}\hat{x}} + {E_{y}\hat{y}}} = {{\frac{1}{k_{x}^{2} + k_{y}^{2}}\left\lbrack {\left( {{\hat{x}\frac{\partial}{\partial x}} + {\hat{y}\frac{\partial}{\partial y}}} \right)\frac{\partial{Ez}_{2}}{\partial z}} \right\rbrack} +}}\quad} \\{j\quad{\omega\mu}_{0}\hat{z} \times \left( {{\hat{x}\frac{\partial}{\partial x}} + {\hat{y}\frac{\partial}{\partial y}}} \right)H_{z}}\end{matrix} \\\begin{matrix}{{{{H_{x}\hat{x}} + {H_{y}\hat{y}}} = {{\frac{1}{k_{x}^{2} + k_{y}^{2}}\left\lbrack {\left( {{\hat{x}\frac{\partial}{\partial x}} + {\hat{y}\frac{\partial}{\partial y}}} \right)\frac{\partial{Ez}_{2}}{\partial z}} \right\rbrack} -}}\quad} \\{j\quad{\omega\mu}_{0}\hat{z} \times \left( {{\hat{x}\frac{\partial}{\partial x}} + {\hat{y}\frac{\partial}{\partial y}}} \right)E_{z}}\end{matrix}\end{matrix} \right\} & (2)\end{matrix}$where

-   -   {circumflex over (x)}: x-direction unit vector    -   ŷ: y-direction unit vector    -   {circumflex over (z)}: z-direction unit vector

FIG. 7 is a characteristic diagram of the amount of electromagneticenergy plotted against the relative dielectric constants of FIG. 6. Asshown in FIG. 7, the amount P_(upper) of electromagnetic energytraveling toward the upper hemisphere (z>0) and the amount P_(lower) ofelectromagnetic energy traveling toward the lower hemisphere (z<0) areexpressed as equation (3): $\begin{matrix}{\left. \begin{matrix}{P_{upper} = {{Re}\underset{{{- \infty} < k_{x}},{k_{y} < \infty}}{\int\int}{\hat{z} \cdot \left( {E \times H^{*}{\mathbb{d}k_{x}}\quad{\mathbb{d}k_{y}}} \right.}}} & \left( {z > 0} \right) \\{P_{lower} = {{Re}\quad\underset{{{- \infty} < k_{x}},{k_{y} < \infty}}{\int\int}{\hat{z} \cdot \left( {E \times H^{*}\quad{\mathbb{d}k_{x}}\quad{\mathbb{d}k_{y}}} \right.}}} & \left( {z < 0} \right)\end{matrix} \right\}{where}\text{}{\begin{matrix}{E = \begin{pmatrix}E_{x} \\E_{y} \\E_{z}\end{pmatrix}} & \quad & {H = \begin{pmatrix}H_{x} \\H_{y} \\H_{z}\end{pmatrix}}\end{matrix}{\quad}^{*}\text{:}\quad{complex}\quad{conjugate}}} & (3)\end{matrix}$

FIG. 7 shows the values in equation (3) quantitatively, which areplotted with relative dielectric constant εr as abscissa against theamount of electromagnetic energy standardized by the entireelectromagnetic energy radiated when the entire space is in a vacuum asordinate, in which numeral 36 indicates a line characteristic indicativeof the amount of electromagnetic energy radiated to the upper hemisphereand numeral 35 denotes a line characteristic indicative of the amount ofelectromagnetic energy radiated to the lower hemisphere.

FIG. 7 shows that, the higher the relative dielectric constant, thegreater the ratio of the electromagnetic energy (P_(lower)) radiated tothe lower hemisphere to the electromagnetic energy (P_(upper)) radiatedto the upper hemisphere. Accordingly, when a substance that may bring aloss, such as the human head X or hand palm Y, is present in thevicinity of the antenna 16, a dielectric member having a relativedielectric constant of 1 or more is mounted on the antenna 16 to fillthe side opposite to the human body. This shape can concentrate moreelectromagnetic waves radiated from the antenna 16 on the side oppositeto the human body than without the dielectric member, resulting in arelative decrease in electromagnetic energy loss due to the human body.

However, when the above-described principle of operation is applied toportable telephones, extraneous phenomena due to finite thickness mustbe taken into consideration because an infinite-thickness dielectricmember cannot be mounted to the antenna 16. For example, a principalextraneous phenomenon is a surface wave. The surface wave is acomponent, of the plane wave components of z<0 expressed by theabove-mentioned equation (1), whose angle of incidence defined by thedielectric member and the vacuum space is larger than the critical angle(θc) that satisfies equation (4): $\begin{matrix}{\theta_{c} = {\sin^{- 1}\left( \frac{1}{\sqrt{ɛ_{r}}} \right)}} & (4)\end{matrix}$

FIG. 8 is an enlarged view of a dielectric member, for explaining arefraction phenomenon around the critical angle of electromagnetic wavesradiated from the antenna to a finite-thickness dielectric member inFIG. 6. FIG. 8 shows a state around the critical angle (θc) at which theelectromagnetic waves generated from the antenna 16 propagate in thefinite-thickness dielectric member 32. In FIG. 8, numeral 37 denotes aplane wave component whose angle of incidence is the critical angle,numeral 38 indicates a plane wave component whose angle of incidence isless than the critical angle and which is radiated into a vacuum, andnumeral 39 indicates a plane wave component whose angle of incidence islarger than the critical angle and which becomes a surface wave. Thesurface wave does not carry the electromagnetic energy in the directionof z<0 but propagates on the x-y plane. However, since the dielectricmember 32 mounted on the antenna 16 is finite in area also for the x-yplane, the generated surface wave is dispersed or reflected at the end.

FIG. 9 is an enlarged view of a dielectric member for explainingreflection and refraction phenomena at the end of the dielectric membercaused by a surface wave component traveling in the dielectric member inFIG. 8. As shown in FIG. 9, a surface wave component 40 is divided intoa surface wave component 41 refracted by the dielectric member 32 intodispersion and a surface wave component 42 reflected into the dielectricmember 32. The generation of the surface wave components 41 and the 42may decrease the function of the dielectric member 32 as a directionalantenna that radiates electromagnetic waves in the direction of z<0. Amethod for preventing the occurrence of the surface wave components 41and 42 is to provide a curved surface on the dielectric member 32.

FIG. 10 is an enlarged view of a dielectric member for explaining adirection in which an electromagnetic wave travels when the dielectricmember in FIG. 6 has a curved surface. As shown in FIG. 10, in thehemispherical dielectric member 17 structured by forming a curvedsurface on the dielectric member 32 shown in FIG. 9, there is a planewave component 44 which passes outwardly through the dielectric member17 and a plane wave component 43 which total-reflects at an incidenceangle θ larger than a critical angle (θc) of the dielectric member 32having no curved surface (θ>θc). A numeral 45 denotes a tangent. Thatis, when the curved surface is provided on the dielectric member 32, theincidence angle θ becomes less than the critical angle θc (θ<θc) andtherefore the plane wave component 44 passes into a vacuum space.Although the dielectric member in shape of hemisphere having a curvedsurface is used in this case as an example having a curved surface, adielectric member in shape of hemicylinder may offer the same effects.Also, other-shaped dielectric members having a curved surface providethe same effects.

Another additional effect caused by the finite thickness of thedielectric member 32 may be the generation of a component that isreflected by the surface of the dielectric member within the criticalangle (εc), then passes through the surface (z=0) including the antenna16, and is radiated to the upper hemisphere (z>0). This component has anamount depending on the thickness and size of the dielectric member, andso is hardly quantified theoretically. Accordingly, numerical simulationis used to optimize the dielectric constant and structure of adielectric member to be mounted.

FIGS. 11A and 11B are a front view and a side view of a portabletelephone for explaining a simulation model in which aninverted-L-shaped antenna is used in FIGS. 3 and 4. As shown in FIGS.11A and 11B, the simulation model is a simplified model in which theeffectiveness of the embodiment is verified by using finite differencetime domain (FDTD). In FIGS. 11A and 11B, numeral 50 denotes a portabletelephone, numeral 51 an inverted-L-shaped antenna mounted on the top ofthe casing, numeral 52 an inverted-L-shaped antenna mounted on thebottom of the casing, numeral 53 a dielectric member in shape ofhemisphere, numeral 54 an antenna feeding section mounted to the bottomof the casing, symbol X a sphere having a radius r (=10 cm) thatimitates the head of a talker, and symbol Y a rectangular prism thatimitates the hand of the talker, wherein concrete values of m are m1=15cm, m2=4 cm, m3=0.6 cm, m4=0.9 cm, m5=2.8 cm, m6=m7=1 cm, m8=10 cm, m9=2cm, and m10=5 cm.

The portable telephone 50 for this analysis has a rectangle casing of 0in thickness and has the inverted-L-shaped antennas 51 and 52 on the topand bottom.

More concrete model of the rectangular prism Y, imitation of a hand, ofthe portable telephone 50 will be described.

FIG. 12 is a perspective view of the portable telephone for explainingthe simulation model in which the palm and fingers of the talker areimitated in FIGS. 11A and 11B. As shown in FIG. 12, the portabletelephone 50 and the rectangular prism Y of the imitation of a hand inFIGS. 11A and 11B can be modeled practically in U shape. The rectangularprism Y is composed of rectangular prisms Y1 and Y2 that imitate thefingers and a rectangular prism Y3 that imitates the palm of a hand.Their concrete numerical values are n=n2=n3=2 cm, n4=4.0 cm, andn5=n6=n7=1 cm. Numerical values of m1 to m5 have been described in FIGS.11A and 11B. In this drawing, the inverted-L-shaped antenna 52 mountedto the bottom of the casing is hidden by the palm Y3.

FIG. 13 is a characteristic diagram of the relationship between relativedielectric constants and electromagnetic radiation efficiencies forexplaining the analysis of the simulation model in FIGS. 11A, 11B, and12. As shown in FIG. 13, the simulation model using the hemisphericaldielectric member is the analysis of the radiation efficiency of anantenna in the case in which the relative dielectric constant of thehead is 43.2, the conductivity is 1.25 (S/m), the relative dielectricconstant of the hand is 36.1, the conductivity is 1.0 (S/m), the casingand the antenna are given perfect conductivity, the relative dielectricconstant of a dielectric member mounted to the antenna is set at 1, 17,20, the conductivity is set at 0, and an alternating voltage of 1V isapplied only to the antenna mounted to the bottom of the casing at afrequency of 2 GHz. A relative dielectric constant of 1 is equal to thatof an antenna without a dielectric member. FIG. 13 shows radiationefficiency increment with the radiation efficiency for a relativedielectric constant of 1 as the reference (0 dB) in decibel. Thisclearly shows that the radiation efficiency (dB) of the antenna of thismodel depends heavily on the relative dielectric constant of thedielectric member.

For example, in this hemispherical dielectric member model, theradiation efficiency of the antenna is increased to a level about 2 dBhigher than that without a dielectric member, or when the relativedielectric constant is set at 1 (0 dB), by setting the relativedielectric constant of the dielectric member at 17 (approximately 2.2dB) or 20 (approximately 2.7 dB).

As has been described, since the portable telephone according to thepresent invention can provides a transmission antenna with a power lossdue to a human body small by mounting a dielectric member with arelatively high relative dielectric constant and little loss on theopposite side of a section covered by the head or the hand of a talker,or in some cases, by providing a curved surface on the dielectricmember, the advantages of providing a higher antenna gain during talkingand therefore of improving the talking performance of a portabletelephone.

It will be obvious to those skilled in the art that the presentinvention is not limited to the above-described embodiments but theembodiments can be modified variously within the sprit and scope of thepresent invention.

1. A portable telephone comprising an upper casing provided with aspeaker and a display screen and a lower casing on which a keyboard isdisposed, wherein an antenna is mounted on at least one of an upper endof the upper casing and a lower end of the lower casing, wherein adielectric member with a predetermined dielectric constant and littleloss is mounted on a back side or a front side of the antenna.
 2. Theportable telephone according to claim 1, wherein the dielectric memberis a dielectric member in shape of hemisphere.
 3. The portable telephoneaccording to claim 1, wherein the dielectric member is a dielectricmember in shape of hemicylinder.
 4. The portable telephone according toclaim 1, wherein the dielectric member is a dielectric member in shapeof rectangular.
 5. The portable telephone according to claim 1, whereinthe dielectric member has a curved surface on a side opposite to theantenna.
 6. The portable telephone according to claim 1, wherein theantenna is a built-in antenna built in the upper casing or the lowercasing.
 7. The portable telephone according to claim 1, wherein theantenna is a dipole antenna.
 8. The portable telephone according toclaim 1, wherein the antenna is an inverted-L-shaped antenna.
 9. Theportable telephone according to claim 1, wherein the antenna is amonopole antenna.
 10. The portable telephone according to claim 1,wherein the antenna is a meander antenna.